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In this experimental work the main focus is on the impact of a single drop of a very viscous liquid onto a thin, horizontal wall film of different liquid. Splashing resulting from drop impact onto a wetted wall occurs in many natural and engineering applications like in internal combustion engines and spray cooling. While the splashing threshold for low viscosity liquid drops has been extensively examined, impact of a very viscous drop is much less studied. The viscosities of drop and wall film liquids are varied up to kinematic viscosities of 100,000 mm²/s. The liquids used in the experiments are miscible. The impact outcome is determined by the impact parameters and fluid properties. The effect of very viscous liquids used as drop fluid and as wall film liquid on the kinematic of the corona expansion is investigated in the experiments. The results of drop impact onto solid walls are compared to obtain the limiting asymptotic values for the splashing threshold. Finally, a semi-empirical model for the splashing threshold, for the maximum spreading radius Dmax and for the maximum spreading times tmax are developed for extremely viscous liquids. Keywords Drop impact, high viscous liquids, wetted wall IntroductionSplashing as a result of a drop impact onto a thin liquid film [1][2][3] or onto a dry substrate [4-6] occurs in many natural and engineering applications like spray coating, spray cooling, paint spraying, ink-jet printing and in internal combustion engines. Impact of a supercooled drop onto a surface of an aircraft can lead to ice accretion, while collision with a heated substrate can lead to drop evaporation or intensive boiling [7]. The drop/wall interaction is affected by the fact that the drop and the liquid film are different liquids and may exhibit different degrees of miscibility and viscosity. A comprehensive review on the phenomena, modeling and application of drop impact can be found in [8]. Drop impact onto a wetted wall can lead to various different outcomes. In the case of splashing

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